Multispacecraft observation of electron pitch angle distributions in magnetotail reconnection
Multispacecraft observation of electron pitch angle distributions in magnetotail reconnection
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DOI：
10.1029/2009ja014553
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发表时间：
2010
影响因子：
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通讯作者：
Rongsheng Wang;Q. Lu;Can Huang;Shui Wang
中科院分区：
文献类型：
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作者：
Rongsheng Wang;Q. Lu;Can Huang;Shui Wang
在本文中，我们给出了在没有明显引导磁场的情况下磁尾重联事件的星系团观测，并分别分析了X线附近和流出区附近的电子俯角分布。在X线附近，在较低的能量下，分布是高度各向异性的（场向双向各向异性），而在较高的能量下，观察到电子沿着磁力线从X线流出。电子分布在流出区变化很大。在流出区边缘，能量较低的电子流向X线，而能量较高的电子则远离X线。当卫星接近电流片中心时，在较低能量下，电子具有场向双向分布，而在较高能量下，电子分布是各向同性的。通过对二维细胞内粒子模拟得到的磁重联电场和磁场中的典型电子轨迹，解释了这种分布的产生机制。结果表明，在X线附近和流出区观测到的远离X线的高能电子是由于X线附近重联电场的加速作用造成的，而较低能量的场向双向分布是由重联部位的磁镜作用造成的。当电子的陀螺半径与磁力线的曲率半径相当时，流出区高能处的各向同性分布是电子随机运动的结果。
[1] In this paper, we present Cluster observations of a magnetotail reconnection event without the presence of an obvious guide magnetic field and analyze electron pitch angle distributions in the vicinity of the X line and the outflow region, respectively. In the vicinity of the X line, at lower energies the distributions are highly anisotropic (field-aligned bidirectional anisotropic), while at higher energies, the electrons are observed to flow away from the X line along the magnetic field lines. The electron distributions change largely in the outflow region. At the edge of the outflow region, at lower energies, the electrons flow toward the X line, while the electrons at higher energies are directed away from the X line. When the satellites approach the center of the current sheet, at lower energies, the electrons have field-aligned bidirectional distributions, while at higher energies, the electron distributions are isotropic. The generation mechanisms of such distributions are explained by following typical electron trajectories in the electric and magnetic fields of magnetic reconnection, which are obtained in two-dimensional particle-in-cell simulations. It is shown that the observed high-energy electrons directed away from the X line both in the vicinity of the X line and in the outflow region are due to the acceleration by the reconnection electric field near the X line, and the field-aligned bidirectional distributions at lower energies are caused by the effects of the magnetic mirror in the reconnection site. The isotropic distributions at higher energies in the outflow region are the results of the electron stochastic motions when their gyroradii are comparable to the curvature radii of the magnetic field lines.